Water cooler



March 1952 A. SELIGMAN WATER COOLER Filed July 12, 1949 IN VEN TOR.

Patented Mar. 4, 1952 U N IT ED S TATES PATENT Q'FF [CE CGOLER ArthurQSeligman, Newark, N. -J.

Application July 12, 194:9,Se1i22l' N0. 104,251

(Cl-62"l'125) 4 Claims.

This invention relates to a refrigerating'system with a secondary "cycle whose condenser is cooled by "a primary source of cold, asegra'sub'stance, or' mixture of substances melting cr -evaporating at low temperature; usually this substanceisrecirculated in a closed primary refrigerating were,

which may consist of any or the" conventional systems, compression orabsorption,"'and may use any of the conventional"refrigerating'niedia.

' The secondary cycle is very simple in'its' design, having no compressor or"absorber, but 'using gravity as motive power for the"ci-rculation of the refrigerant, and. it is characterized'b-y the is at a temperature low enough to accomplish'the V purpose of the cooling operationfbut never'below a safe degree, regardless of possible wide variations of the evaporator temperature of the primary cycle, and regardless of tlie amount'of heat withdrawn in the secondary evaporator. The invention may be used, but is, of course, not restricted, to combine .a water cooler with a household or a small commercial refrigerator. In these refrigerators trays forfree'zing ice. cubes are usually provided, and in many cases also low temperature storage compartments; the evaporator temperature must, therefore beLkept considerably-below the freezing point of water; even without these. accessories the desire to avoid excessively large coolingsurfaces would call fora low evaporator temperature; the; standard practice. isjtherefore, to operate the evaporators at about 18 F.

On the other hand, in water coolers theevaporator temperature must be kept slightly above '32 'F. to avoid the formation of ice.

"It is, thus, notpossible to use a part of the evaporator of a refrigeratordirectly'for water cooling. Even if the heat exchanging surface were made very small, or if an obstacle were. put in the path of heat transfer, suchwas a layer of material of low conductivity, the dangerof-a freeze-up could still not be eliminated-in case no water were withdrawn for a considerable length of time. If the'water cooler were .not in direct contact with the evaporator, butplaced within the refrigerator in heat exchange with the cold air, freezing-wouldbe avoided, inias much as the cabinet temperature is usually kept above 32 F.; but the heat transmission coeffi 'cientfrom still air is so low that a veryilarge surface would be needed to attainsufficientcapacity.

The present invention allows to build a water cooler in combination with a refrigerator, which has 'a good heat transfer" to insureia' satisfactory 2 chilling-When a large number of drinks istaken in rapid' succession, and which yet-is absolutely safe against-freezing when no water is with drawn forany-length of :time.

I he --accompanying drawings illustrate the principle.

'- Fig. i -shows "a section through the essential parts *of the--device,-servi-ng' as 1 a water cooler integrated --i-n a household refrigerator, "whereas Fig. 2: shows in section another variation ofthe device proper only, i. -e.-w'ith --all-other parts omitted-emeptthe primaryevaporator coils.

Referri-ng to -Fig. '1, the water is==supplied through-pipe lin'el from-an-inverted"glass jar 2; this is, =of-course,mot-essential to the invention; for-instance, the line I --may-be rdirectly connected-to'the city water' supply, and, naturally, beverages other than Water may be-cooled just-as well. The water passes through the coil 3,- Where*it *i'schilled, and is withdrawn, as'required, from the faucet 4. The coil-3- is located inthesecondary evaporator 5 and immersed in thesecOnda-r'y refrigerant boiling therein, thus absorbing heat fromthe water. The'refrigerant 'vaporspass-through the suction line 6 tothe seconda-ry'condenser l, wherethey are'condensed by' -the' primary source of cold, viz. apart of the coils or the primaryevaporator't. The liquefied refrigerant assembles in thereceiver'll, Whichis located below the condenser and in unrestricted communication with it, until the liquidreaches the overflow l 0, from which it"flows through the liquid'linell back to "the secondary evaporator. It-will-be "noted'that' the last part 'of' thesuction line 6' is bent downward and that its 'open end I2 is near "the bottom'of'the condenser receiver. The vapor on its way fromtheevaporator to the condenser ...must, thus, overcome a static head, which is determined by the immersion H, .i.. e..the vertical distance from the opening '12 of the suctioniline tothe overflow I0. Thus, the. pressure, andconsequently the temperature, in the evaporatorlmust at all times be higherthan in the condenser; when not enough water passesTth-rough thev coolerto bring the refrigerarit to a boil under this pr'edeterminedpressure, evaporation and further chilling of the water will stop.

The primary evaporator-e is, of. course, a part of the well known refrigeratingsystem, whose "high side"'l3 is not shown iii-detail, and whose accessories, such as thermostatic control, are

omitteddor simplicitys. sake, as they are. obvious tothose familiar with the art. For the same reason the insulationof. the refrigerator is not shown. It may, however, be mentioned that the secondary evaporatorm'ay be arranged either inside-the mainainsulation .(it need not. be insugreat amount of freedom in locating the secondary evaporator. It is only required that the difference L between the liquid levels in receiver and evaporator is by a safety margin R greater than the immersion H to insure the return of the liquid, and that the highest point of the suction line is by a safety margin S higher than the overflow 10 to prevent back fiowythe faucet 4, of course, must be at a lower level than the water supply 2.

In the variation shown by Fig. 2 the evaporator is placed in close vicinity to the condenser. Corresponding parts are marked with the same symbols as in Fig. 1. The water enters from a suitable supply through valve [4, which, of course, can be kept open all the time during normal operation. A layer of insulating material 55 is provided to prevent direct heat exchange from the water to the cold liquid refrigerant in the condenser. In this case the boiling refrigerant is confined within the pipe coil of the evaporator, the water is in the outer shell, where suitable bafiles may be arranged to guide it on a serpentine path; this arrangement is preferable where finned r bristled tubing is used, as for well known reasons the fins are to be on the side with the lower heat transfer coefficient.

It has been stated above that a number of refrigerants are available for the secondary cycle; the following discussion shows how for given operating conditions a proper substance may be selected and the principal dimensions of the apparatus may be determined.

It is assumed that a capacity of 100 B. t. u./hr. is required, that the secondary evaporator temperature be 40 F., and the condenser temperature 18 F. The three substances carbon-tetrachloride, ethyl-alcohol, and methyl-alcohol are to be investigated. For brevitys sake certain simplifications and approximations have been used in the following, which, however, do not essentially influence the result.

In the attached tabulation the values of freezing points, latent heats, and densities resp. as entered on lines 3, 6, and 8 were taken from competent handbooks. It i known that for most substances the relation between vapor pressure p and absolute temperature T can be expressed by the equation wherein a and K are constants; by analyzing the experimentally found vapor pressures at various temperatures from the best available sources, values of these constants could be determined and entered on lines 4 and 5 resp. referring to inches of mercury and degrees Fahrenheit absolute as units. Therefrom the vapor pressures p" at seven temperatures, which are of interest in this investigation were calculated. On lines 9 to 15 are tabulated the columns of liquid 7!. of each substance equivalent to its vapor pressure at these seven characteristic temperatures; to get these figures from the vapor pressures is, of course, simply a matter of converting into an-, other unit, viz.

wherein the figure 850 represents the specific weight of mercury. In the actual operation of the apparatus the temperature of the liquid line H is somewhere between the condenser temperature of 18 and the evaporator temperature of 40; inasmuch as the density of the liquid varies very little between these limits, the error committed by using the density at 32 is negligible.

In the absence of direct experimental data the vapor densities at 40 were approximately calculated as though the substances were ideal gases, which is exact enough for the intended comparison; the density of an ideal gas is wherein lc depends on the units and is 23.3 in our case; see line 7.

Now, by simply subtracting the liquid columns for the condenser temperature (line 11) from those for the evaporator temperature (line 14) the decisive figure for the design is arrived at, namely the height of the immersion H (line 16).

In order to investigate more closely the operating characteristics the gradients of the vapor pressure at the operating temperatures are given on lines 17 and 18, that is the variation of pressure for 1 F. variation of temperature, or mathematically speaking the first derivatives of the pressure with respect to the temperature, which are, of course, easily arrived at by differentiating Equation 1, namely Comparing the gradients at 40 and 18 furnishes an important characteristic, as will be discussed later; see line 19. As stated above, the normal condenser temperature i supposed to be 18, and the apparatus is so designed as to render the evaporator temperature 40 under this condition. It may now be investigated what happens when the condenser temperature varies. It may be assumed that the control of the primary cycle allows a decrease or increase of 4, 1. e. a variation from 14 to 22. In as much as the pressure differential between condenser and evaporator must remain constant, name1y II, it is simple to calculate the corresponding evaporator pressures, as indicated on lines 20 and 21. By means of either the gradient G 0 or of Equation 1 the corresponding evaporator temperatures can easily be computed as shown on lines 22 and 23.

To avoid a freeze-up the evaporator temperature must not fall below 32. The condenser pressures which would have to be reached in order to bring about this condition are listed on line 24, and the corresponding temperatures on line 25. It may be mentioned that the actual temperatures of the primary refrigerant would have to be even lower than these figures to cause a freeze-up because of the necessary temperature drop on and through the heat exchanging surfaces.

The liquid column L must not only counterbalance the static pressure difierential between evaporator and condenser, but also provide a slight excess to impart a sufficient velocity to the vapor in the suction line 6 and thus keep the system in motion. To create a velocity in a pressure drop of XY"40 P is required, g being the acceleration of gravity. A velocity of 2000 ft./min. for instance would thus require a pressure drop of rhe correspending'nqum commns are ttviossly given on line 27; it is obviously 1 (7) fiox'y' io Finally on the last line the necessary diameters of the suction line are listed, assuming for comparisons'sake acapacity of 100 B. t. u./hr. and a vapr velocity of 2000 amm -Weare now ready to-discuss the selection-of a proper refrigerant.

Within the contemplated working range the vapor pressures of ethylalcohol, methylalcohol, and carbontetrachloride, as computed by Equation 1 have a ratio of approximately 1:213. In as much as all of them, however, are of the magnitude of one inch of mercury, there is no decisive advantage on this count for any of the three substances, although the higher pressure of carbontetrachloride may be regarded as slightly favorable, because very small traces of air remaining after evacuation will be the more negligible the higher the partial pressure of the refrigerant.

Line 8 shows that the amount of refrigerant required to properly fill the system is about twice as much for carbontetrachloride as for'ieither of the alcohols. As -o'n'ly sniall quantities are involved and allg three substances are rather com- -the-final' choice. mlso -the fact that the alcohols areinflammabla' iwhereas carbontetrachloride is 'not,-'w.ill not -'be'=*absolutely decisive in view of the --small=:quantities' and of the fact that the system :is under-vacuum.

-As- .-seen 1 from line 16, the condenser. must be located about twice" as high above theevaporator -in the ,case of methylalc'ohol as foreither of the other refrigerants, which may be a disadvantage where a very compact construction is desired.

Line l9-shows thattliere-is only a-very small -differencebetween the three substances with respect to-sensitivity-that is to the variationof evaporator temperature fora given variation of condenser temperature. ,Line 25, however, shows that the ultimate safety margin is considerably better 'for methylalcohol than for carbontetrachloride, in as much as for'a freeze-'up'the condenser temperature will have to fall abt. 9 deeper.

Line 27 finally reveals that ethylalcohol requires the circulation of a vapor volume about twice as Refrigerant Symbol Property igg Unit Carbom tetra Ethyl- Methylchloride alcohol alcohol Formula C014 0 H O CH 0 Molecular Weight" 154 2 46 $2 Freezing Point -73 237 208 7. 8. 15 8. }Constants in equation (1) 3, 230 3 700 3' 875 Heat of Evaporation at 40. t. u./lb 93. 5 411 520 Denslty Vapor at 40 Equ(3) lb./cu. ft. .0232 0026 0041 Density Liquid at 32 lb./cu. ft 102 50.2 50. 5 olumn 5 2. 8 6.0 of Liquid 14 4. 2 8. 8 equiva- 18 4. 9 l0. 2 lent to 22 Equ(2) 5. 6 11.5 Vapor 32 7. 9 l7. 5 Pressure 40 10. 5 23. 7 at 50 14. 9 33. 3 Difference between 40 hm-ML- 5. 6 13.5

and 18. I Gradient at 40 Equ(4).. 36 .85 Gradient at 18 Equ(4) 18 40 Ratio of Gradients (ho/ 15" 2. 0 2.1 20-. h Erllz porator Pressure at n+ 9. 8 22. 3 21.. [IV-13..-- conggr iser Temperature hz2+H ll. 2 25.0

o 22.- tv Eva izigator Temperature Equ(1).. 38.1 38. 4

a 23.. t (lorfnzignser Temperature 41. 9 41. 5

o 24-. hc-sp Condenser Pressure at 32 hag-IL inch Liqu... 4. 6 2. 3 4. 0

Evaporation. 25.. $042... Condenser Temperature Equ(l). F 5. 6 5 -3 at 32 Evaporation. 26-. Ah Haifa? {or 2,000 ft./min. Eqn(6a) inch Liqu..- .05 013 018 e 001 y. 27.. v Vapor Volume per B. t. u. EquQ)" cu.ft./B.t.u- 46 91 48 2a-- a Diameter of Suction Line .394 v inch .26 .37 .27

for B. t. u./hr. and 2,000l't./min.

I claim:

1. Method of controlling the evaporator temperature of a secondaryrefrigerating cycle in which a liquid refrigerant is evaporated to produce the cold, its vapors subsequently re-condensed at a higher level at lower temperature and pressure, and the liquid fed back to the evaporator by gravity, whereby a constant difference between condensing and evaporating pressures is maintained by passing the vapor on its way from evaporation to condensation through a column of the liquid refrigerant, which is held at a'constant height.

2. Refrigerating apparatus, consisting of an evaporator, a receiver located at a higher level than the evaporator, a condenser located at a higher level than the receiver and in unrestricted communication therewith, a liquid return. line leading from the top of the receiver to a point near the bottom of the evaporator, and a suction line leading from the top of the evaporator to a point higher than the top of the-receiver and down again into the receiver near its bottom.

3. Refrigerating apparatus as specified in claim 2, in which the vertical distance H between the connections of the suction line and of the liquid return line to the receiver is so chosen as to create the desired pressure diiierence, and the vertical distance L from the connection of liquid return line and receiver to the top of the evaporator is at least of the same length.

4. Refrigerating apparatus as specified in claim 3, particularly for chilling aqueous fluids, in which said vertical distances are of sufficient height as to ensure an evaporator temperature above 32 F. at the lowest possible condenser temperature ARTHUR SELIGMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,188,476 Knight Jan. 30, 1940 

